Energy Efficiency: The Green Catalyst

After you have turned the key on a finished remodeling job, and paid off your subs and yards, what really makes the project green is its energy efficiency.

Sure, paint choice is important. Carpets matter, too, because they can off-gas. And your green intentions should be expressed in your choice of wood, foam, insulation, and floor finishes, to say nothing of the windows you have spec'd, and the plumbing, light fixtures. But after all the positive impact of these products has been accounted for, what’s really green about a home is how much fuel it uses to heat and cool over its lifetime.

I am not saying these other items are not important. They are. They are essential. But where you really “move the needle,” where you have the greatest long-lasting impact, is when you design a project with a high-integrity, thermal envelope that controls moisture, maintains good indoor air quality and cuts down on fuel consumption.

Here’s why: There are number of ways to calculate a home’s carbon footprint. That’s the amount of carbon-dioxide, CO2, pumped into the atmosphere by human activities like eating, driving, and — mostly — heating and cooling a home. The per-home CO2 contribution is measured in tons per year, and a typical American household can easily contribute between 50 and 70 tons each year for just normal activities. Over 50 years, that household is contributing 3,500 tons of CO2.

Let’s focus on the thermal envelope to see how to reduce that. What products would have a measurable effect? Though remodelers have little control over how a house is oriented toward the sun, you can start with soffit lengths that are geared toward reducing solar gain in hotter months. The length is a factor of your latitude. Google the phrase overhang length and solar gain to find regional online calculators.

Next consider lighter colored, reflective roofs. Three-tab products have these properties now, and they can markedly reduce cooling loads. Look for the Energy Star rating and consider a permeable roof underlayment. Radiant barriers integrated with sheathing can reduce solar radiant heat gain, too. For windows, look for Energy Star windows, and — for the love of Pete — visit nfrc.org/label.aspx and take 15 minutes to learn how to read (and explain to your client) the NFRC window label.

Greening up wall and roof systems is as much about design as product choice. Use scissor trusses (a.k.a. “energy trusses”) that offer more room for insulation where the bottom chord hits the wall’s top plate, and use insulation strategies (different from just cramming batts into stud bays) that reduce “wind washing,” where even moderate wind can rob the wall of a remarkable amount of R value. Always provide framing design that allows for careful foaming in around utility penetration, windows and door.

Wall systems also offer a wide range of green options, from ICFs and SIPs to stick-built homes that are wrapped with increasingly sophisticated, drainable house wraps and insulated with spray foams or Energy Star-rated insulation.

At this point you may be saying, “Well, this green building isn’t anything new. I’ve been remodeling like this since 1985!” For quality-minded remodelers, that’s very true. Except for a deluge of green products coming onto the market, and heightened awareness to green by everyone from homeowners to code officials, green building is about quality building. I was profiling green builders in the late '80s when I wrote for the Journal of Light Construction. I remember interviewing one builder who built SIP walls two-and-half stories up, and hung all interior floors on a ledger, so nothing but windows and doors penetrated the thermal envelope. I recently interviewed a young green builder who was doing the same thing, and he proudly told me about this great new innovation he’d come up with. Go figure.

Next improve the HVAC appliance and the forced-hot-air duct system, which should have sealed seams and be run through conditioned spaces. The HVAC unit has the greatest impact on the home’s carbon footprint because it will heat and cool the home for years to come. You have an ace-in-the-hole when spec'ing up-market HVAC units and prompting your client to step up to a high-efficiency model: the cost of fuel. An extra $1,000 spent on a high-efficiency “balanced” HVAC system (which conditions fresh air with the heat from outgoing air) will be easily recovered over its operating lifetime.

You can green up lots of other areas of the house, too. Use CFLs for lighting (and watch for very viable LED lighting in the next year or two) and Energy Star appliances. As you seek guidance from NAHB’s National Green Building Standard and whole-house rating system or LEED-H, you’ll find that my recommendations are embedded in the features that they like to see in green homes. But after you read all the manuals a you’ll find that you’ll still be building quality, low-toxic homes — something you may have been doing all along.